The engine shuts down by itself while flying

The Reality Expansion Pack simulates the failures of a real engine.
For example, you should not overboost the manifold pressure or run the engine over a certaing amount of power for too much time.
Do not run the engine at high RPMs when the CHT is too low.

You must always refer to the engine limitations reported in REP’s manual.
For the Cessna 210 the major limitation you get is 36 InHg of manifold pressure and 2700 RPM for a maximum of 5 minutes.